Mechanical face seals are described above in European patent application EP 1 209 386 A1.
A counter ring can rotate with respect to the mean sliding surface diameter at sliding speeds of up to 200 m/s relative to the stationary face seal ring. At high sliding speeds, viscous friction in the sealing gap leads to a considerable heat input into the face seal ring and into the counter ring. Axial temperature gradients in the face seal ring and in the counter ring can cause severe deformation of the rings. The geometry of the sealing gap can change in an undesired or impermissible manner, specifically, in terms of the height of the sealing gap as well as its V-shaped widening.
European patent application EP 1 209 386 A1 describes providing a rotating counter ring with an axial projection in order to compensate for thermally caused warping of the rotating counter ring.